The present invention generally relates to methods and apparatus for centering rotating components within their stators and, more specifically, to methods and apparatus using non-concentric rings for reduced turbo-machinery operating clearances.
Performance of turbo machinery depends upon operating clearances of rotating components, such as aerodynamic components, in relation to their stators. For aerodynamic components, tighter clearances between the rotating component and its associated stators results in higher efficiency resulting in less fuel burn and more power. Operational clearances are affected by the ability to radially center rotating components within their associated stators. Rotating components may consist of aerodynamic components, such as impellers, compressors, turbines, and seals, or may consist of electric machines and bearing journals. Tighter geometric control of parts at increased cost is often required to reduce the variation in build clearances due to part runout control.
Referring to FIG. 1, there is shown a conventional turbo machine 10. A forward (cold) end 12 may house a first bearing compartment 14 and an aft (hot) end 16 may house a second bearing compartment 18. While not limited to such, the turbomachine 10 of FIG. 1 has two turbine rotors 20 and a shaft 22. The turbines 20 are contained within the turbine static structure 24 forming a clearance 36.
Several parameters may affect the operating clearances 36 of the turbine rotors 20 relative to the static structure 24. These include the dimensional tolerance of the component, e.g., turbine rotor, the operational range of the turbomachine (e.g., speed, temperature, altitude and power), and the ability to center the rotating component(s) (such as turbine rotors 20) within its static structure 24, such as a turbine shroud.
Component tolerances in areas where the clearances need to be controlled between rotating and static components are often held very tight. Conventionally, these rotating and static components may be match-machined to minimize the effect of this variable. Advanced analytical tools and design processes have resulted in the ability to control the clearance between parts during the various operating conditions for which the machine is to be used.
Control of the concentricity of the rotating component to the static component may depend upon the geometric controls of the components that are within the path (stack) of the rotating component and the static component. Rotating components require tight geometric tolerances in order to operate without excessive vibration. However, the static components, being larger and more complex, are often not able to have tight geometric controls, potentially resulting in an offset between the rotating and static components.
The basic effect of this radial offset is shown schematically in FIG. 2, where a shaft centerline 26 of shaft 22 may lack concentricity with a turbine shroud centerline 28 of turbine shroud 24. This may result in a circumferential variation in clearance, which can be referred to as a non-uniform clearance, between the rotating components (in this case, the turbine 20) and the static component (in this case, a turbine shroud 24). This variation in clearance may result in a small turbine clearance 30 and a large turbine clearance 32 within turbine shroud 24. A radial cross-sectional view of this offset is shown in FIG. 3.
The current state of the art offers three basic approaches to concentricity between rotating components and static components. The first approach suggests operating with larger than desired clearances, thereby accepting lower machine performance. The second approach suggests improving the geometric control of the static components, however at a significant increase in component cost. The third approach involves match-set machining the static component to the rotor component, again at an increased cost and the creation of match, non-interchangable, sets.
U.S. Pat. No. 6,309,177, issued to Swiderski et al., uses a single non-concentric ring to center a turbine stator (static component) relative to the turbine rotor (rotating component). A single ring has limited ability to correct for non-concentricities between a rotating and non-rotating component. The '177 patent uses rings with different degrees of non-concentricities to improve its ability to adjust the turbine stator relative to the turbine rotor. This is accomplished by measuring the eccentricity (runout) between the turbine stator and turbine rotor and selecting the appropriate non-concentric ring. This also resulted in match set hardware and if a component is replaced, a different ring might be required to maintain a uniform clearance.
U.S. Pat. No. 4,222,708, issued to Davison, uses a pair of frame components with annuluses which have outer and inner surfaces that are relatively eccentric to each other. Each frame component has two radial pilot features that are non-centric to one another. The '708 patent addresses the position of the shroud centerline relative to the rotor centerline to make a single rotating component concentric within the frame. The '708 patent, as does the '177 patent relates to adjustment of a portion of the static structure centerline relative to the rotor center centerline to minimize clearances.
As can be seen, there is a need for improved methods and apparatus for reducing turbo machinery operating clearances. There is also a need for methods and apparatus to adjust the rotor relative to the static structure, thereby centering a plurality of components on a single rotor/shaft.